This invention relates generally to the field of data storage devices, and more particularly, but not by way of limitation, to adaptive dampening of thermal asperity events for disc drive.
Disc drives are used for data storage in modem electronic products ranging from digital cameras to computer systems and networks. Typically, a disc drive includes a mechanical portion, or head disc assembly (HDA), and electronics in the form of a printed circuit board assembly (PCB) mounted to an outer surface of the head disc assembly. The printed circuit board assembly (PCB) controls head disc assembly functions and interfaces between the disc drive and its host.
Generally, the head disc assembly includes one or more magnetic discs affixed to a spindle motor assembly for rotation at a constant speed; an actuator assembly supporting an array of read/write heads that traverse generally concentric data tracks radially spaced across the disc surfaces; and a voice coil motor (VCM) providing rotational motion to the actuator assembly. With the advent of magneto-resistive head technology, continued demand for disc drives with improved reliability and overall operating efficiencies has caused disc drive manufacturers to seek ways to increase the tolerance of disc drives to thermal asperity events as well as to reduce the effects of thermal asperity events during data transfer functions.
To ensure data is correctly read from a track of the magnetic media in a disc drive, the read/write head should be kept centered on the recording track while maintaining a desired fly height. A collision of the read/write head with foreign objects on the disc media can cause a large shift in the baseline of the preamplifier output, due to a temperature rise of the magneto-resistive head. An occurrence of such an event is referred to in the art as a thermal asperity (TA) event. An amplitude spike in the readback signal is the result or symptom associated with the thermal asperity event, which can cause serious corruption or loss of data during a read function of the disc drive.
Thermal asperity detection is accomplished by sensing the baseline of the signal using both a low-pass filter and a zero-crossing detector. Reducing the effects of the thermal asperity on readback data relies on a pre-set switching dampening factor, carried out by an AC dampening circuitry. However, the specific dampening value of the pre-set switching dampening factor is not always the best value and may cause under dampening and over dampening.
Under dampening the amplitude spike of the thermal asperity event extends the time period for regaining a lock on the readback signal. The thermal asperity causes a read channel of the disc drive to undertake a task of adjusting an automatic gain control circuit (AGC) in preparation for reading data at a higher amplitude. However, when the data following the amplitude spike enters the channel it is at an amplitude below the level set by the AGC and the channel is unable to read the data. This inability to read the data causes the read channel to reset the AGC back to the baseline where, once again, the data can be read.
Over dampening, or reducing the amplitude of the read back to a value below the baseline, results in adjustments to the AGC in preparation for receipt of data at an amplitude below the baseline. However, the data following the thermal asperity event is at the baseline amplitude, an amplitude above the threshold set in the AGC, which causes a loss in data for the period of time that it takes the read channel to readjust the AGC back to a setting consistent with the read data baseline.
Therefore, challenges remain and a need persists for a techniques and an apparatus for adaptive dampening a thermal asperity event during read operations of a disc drive. It is to this and other features and advantages set forth herein that embodiments of the present invention are directed.
The present invention provides a method for adaptively dampening a peak amplitude of a thermal asperity signal in a disc drive to minimize the loss of read data integrity during read operations. The method for adaptively dampening the peak amplitude of the thermal asperity includes the steps of determining peak-to-peak preamble signal amplitude for identifying an amplitude signal range of the peak amplitude of the thermal asperity signal; measuring the peak amplitude of the thermal asperity signal; separating the peak-to-peak preamble signal amplitude into substantially even portions for use in calculating a value of the amplitude signal range of the peak amplitude of the thermal asperity signal; calculating the value of the amplitude signal range of the peak amplitude of the thermal asperity signal for use in determining a dampening resistance used by a dampening circuit to adaptively dampen the peak amplitude of the thermal asperity signal; and activating the dampening circuit to dampen (also sometimes herein dampen down) the peak amplitude of the thermal asperity signal.
The present invention further provides a disc drive having a basedeck supporting a spindle motor assembly with a rotatable disc surface accessed by at least one magneto-resistive read/write head positionably adjacent the rotatable disc surface. A printed circuit board assembly secured to the basedeck is provided with a read/write channel communicating with the magneto-resistive read/write head through a preamplifier; the printed circuit board having a variable gain amplifier communicating with the preamplifier adjusting a signal provided by the magneto-resistive read/write head; a dampening capacitor in parallel with the variable gain amplifier for filtering the signal provided by the magneto-resistive read/write head; and an n-channel enhancement MOSFET in parallel with the dampening capacitor to provide a dampening resistance for dampening the signal provided by the magneto-resistive read/write head.
These and various other features and advantages, which characterize embodiments of the present invention, will be apparent from a reading of the following detailed description and a review of the associated drawings.